3 Answers
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This discussion centers around the mishna in avos towards the end of chapter two (either mishna 12 or 17, depending on your print) "all your deeds should be lishem shomayim".

Rambam offers two different approaches between his pirush on the mishna and in his shmona perakim, which is echoed in the two different approaches in the shulchan aruch brought in shalom's answer. See there and the sources in Shalom's sources for a better understanding.

There is also the gemara in Bava Basra 16a which praises Avraham for having never concentrated on Sarah's beauty, brought in Rashi on Lech Licha 12 11. This would give credence to the no personal enjoyment approach.

This is all Midas Chasidus though. A possibly unattainable goal for which the true benefit is gained simply by a different approach to life. There are many examples in the Talmud where a wife's beauty is appreciated for shalom bayis. In fact the seffer chasidim says it is not allowed to marry someone one finds unattractive as he will spend the rest of his life secretly praying for her to die.

So as with all Midas Chasidus, a disclaimer is in order, not to ruin the main mitzvah while chasing chasing the extra credit. Especially when this mitzvah involves another human being who might not appreciate the lisheim shomayim approach, see the parenthetical story.

(Sad story disclaimer: I had a friend in yeshiva who was the type of masmid who actually learned in his sleep. Seriously. Actual gemara came out of his mouth in his sleep. He impressed all of us cynics. Well, a couple of years into his marriage his wife asked him* what goes through his mind when they were together. He told her all his higher kavanos and all his lisheim shomayim intentions. She divorced him and took the kids.

Ezra and his generation of Anshei Keneses haGdolah tried to put in place legislation requiring a man to go to the miqvah the morning after relations, "so that he should not copulate like a rooster". I don't know if this was an estimate of the right level of annoyance the next morning, or so that the man who did overdue it would pay a social penalty because someone would eventually notice how often he goes. This legislation was never accepted by the masses, and therefore did not become binding. (Shulchan Arukh, OC 88:1)

But the motive behind the attempt tells you something.

Similarly, Nachmanides on "qedoshim tihyu, qi Qadosh Ani -- be holy, for I Am Holy" (Vayiqra 19:2) says that the mitzvah is to avoid being a "naval bireshus haTorah -- a knave with [what would otherwise be] the permission of the Torah". Or, as Nachmanides is explained by Rav Shimon Shkop (introduction, Shaarei Yosher), to avoid those distractions from one's commitment to holiness.

What is knavely behavior? "The person who is driven by appetite (ba’al ta’avah) will find room to indulge in lustful behavior with his wife or his numerous u wives, and to be among those that swill wine and guzzle meat (per Prov 23:20), and will speak freely using all those vulgarities that are not explicitly prohibited by the Torah. ... Therefore this verse comes, after [the Torah] has enumerated those things that are completely prohibited, commanding in a general way to separate ourselves from excessive material indulgence and to restrict ourselves in sexual intercourse, as the Rabbis say, “Sages ought not to be found with their wives like roosters” [Berakhos 22a], but only engage in sexual relations according to that which is needed to fulfill the mitzvot connected therewith."

Those mitzvos being the connecting with another person "and he shall be attached to his wife and become another person" (Bereishis 2:24) and procreation (Bereishis 1:28).

Similar to Rav Shimon Shkop's take on the Ramban, that overdoing it is defined by distractions to holiness, we find Rav Moshe Chaim Luzzatto writing in Mesilas Yesharim (ch. 14) writes (bracketed insertion and emphasis mine):

Separation in relation to pleasures, which we spoke of in the previous chapter [where it is given as one of three types of "separation"], consists in one’s taking from the world only what is essential to him. This type of Separation encompasses anything which provides pleasure to any one of the senses, whether the pleasure be gained through food, cohabitation, clothing, strolls, conversation or similar means, exceptions obtaining only at such times when deriving pleasure through these means is a mitzvah.

So there is a call to refrain from overdoing sex, but the definition of "overdoing" is when it gets to the point that you lose sight of bonding to one's spouse, a very contextual and subjective frequency.

Satmar thought has similar language, by the way. And many other groups feel that's unworkable.

The Shulchan Aruch in Or HaChaim uses very strong language about "only for her", but in Even HaEzer that does not appear. Most notably, the Aruch HaShulchan modifies the Shulchan Aruch's language from "only for her" to "also about her."

That's an approach that I've heard from many contemporary marital educators: in a healthy relationship, it can't be entirely about only one person.

amazon.com/Marital-Intimacy-Avraham-Peretz-Friedman/dp/… -- Marital Intimacy by R' Avraham Peretz Friedman. It's the only book I know that is about the Jewish spirituality of marital intimacy. Not focusing "only" on the laws, nor a book that wraps typical contemporary self-help advice in citations and stories from Judaism.
– Micha BergerDec 10 '15 at 22:21